Disk drive which detects head flying height using a peak count based on a random data pattern

ABSTRACT

The present invention relates to a system for determining whether the flying height of a read/write head above a disk in a disk drive is within an acceptable range, in substantially real time. The system relies on variations in read signal resolution with flying height to make the determination. In one embodiment, read signal resolution is measured and compared to a predetermined threshold value to determine whether the present flying height is in the desired range. In another embodiment, the number of peaks in a read signal that are detected (and/or not detected) by a detector is used to determine whether the head is in the proper flying height range. Because of read signal resolution effects, the number of detected peaks will decrease as the flying height of the head is increased. The system also provides for postponing a transfer of data to/from the disk when it is determined that the head is not within the acceptable range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.09/224,202, filed Dec. 30, 1998, which is a continuation of U.S.application Ser. No. 08/764,340, filed Dec. 12, 1996 (U.S. Pat. No.5,909,330).

FIELD OF THE INVENTION

The invention relates in general to digital data storage devices and,more particularly, to digital data storage devices that utilize a headto transfer data from/to a moving medium.

BACKGROUND OF THE INVENTION

A disk drive is a digital data storage device that stores data insubstantially concentric tracks on the surface of a disk. During theoperation of a disk drive, the disk is rotated at a substantiallyconstant rate while data is written to or read from its surface. Thedisk drive is generally coupled to a host computer that delivers accessrequests to the disk drive whenever the host desires to store orretrieve digital information. To perform an access request, the diskdrive first positions a head above the track of the rotating diskspecified in the access request. Once the head is properly positioned,the requested data transfer (i.e., either a read operation or a writeoperation) is allowed to take place. During a read operation; data fromthe predetermined track is sensed by the head, after which it isprocessed by a read channel and delivered to the host system. During awrite operation, data is received from the host, processed into asuitable format, and then delivered to the head which transfers the datato the predetermined track.

During operation of the disk drive, the head generally rides above thedisk surface on a cushion of air (known as an air bearing) that iscreated by the movement of the disk under the head. The distance of thehead from the disk while riding on the air bearing is referred to as the“flying height” of the head. To produce the “lift” required to hold upthe head, head “sliders” are generally used that have the requisiteaerodynamic qualities. In general, the performance of the disk drivewill depend, to a great extent, on the maintenance of a proper headflying height. That is, performance will be degraded if the actualflying height of the head is considerably higher, for example, than anominal flying height. This is particularly the case during writeoperations where an unexpected increase in flying height can result inwritten data that is unreadable.

A need therefore exists for a method and apparatus for determiningwhether the actual flying height of a head is within a desired range.

SUMMARY OF THE INVENTION

The present invention relates to a system for determining whether theactual flying height of a head is within a desired range. The system iscapable of operating “on the fly” and may therefore be implemented in adisk drive system without substantially increasing disk access times.That is, the flying height determination can be made substantially inreal time, before the head reaches the data sector to be written to orread from. This allows the drive to forego the transfer of data betweenthe head and the disk when it is found that the head is outside of thedesired flying height range, which is generally determined by empiricalmethods. The present invention has application in virtually any type ofdata recording system using either a contact, a pseudo contact, or anon-contact head to transfer data from/to a moving medium. This caninclude, for example, magnetic disk drive systems, magnetic tapesystems, and optical disk drive systems. In one application, theinvention is used in a system utilizing low flying height heads, such asthe Tripad (TM) head manufactured by Read-Rite.

To operate in real time, the invention relies on the relationshipbetween read signal resolution and flying height. Read signal resolutionis a performance measurement that is related to the disk drivers abilityto read information at different frequencies. In this regard, readsignal resolution is generally calculated using the ratio of themagnitudes of two analog read signal portions having differentfrequencies. In conceiving of the present invention, it was appreciatedthat the ability of a read head to read data patterns at higherfrequencies diminishes at a faster rate than the ability of the head toread lower frequency patterns as the head moves away from the disk.Because of this, read signal resolution changes in a predictable manneras the flying height of the head increases. In general, the inventiondetermines a read signal resolution value, or a read signal resolutionrelated value, and then compares the value to a predetermined value todetermine whether the flying height is in the proper range.

In one aspect of the present invention, a disk drive is provided thatcomprises a disk having a first data pattern with a first frequency anda second data pattern with a second, higher frequency on a first track.The disk drive also includes means for reading the first and second datapatterns, using a head at a first vertical distance from the disk, tocreate first and second analog signal portions, respectively. Inaddition, the disk drive includes a determination unit for determiningwhether the first vertical distance of the head is within an acceptablerange for performing a transfer of user data between the first track andan exterior environment using the first analog signal portion and thesecond analog signal portion, wherein the determination unit does notrequire the movement of the head to a substantially different verticaldistance to make the determination.

The determination unit determines whether the first vertical distance iswithin the desired range based on read signal resolution. The readsignal resolution can be calculated by taking the ratio of themagnitudes of the first and second analog signal portions. Thedetermination unit can include a comparison unit for comparing thecalculated read signal resolution to a threshold resolution value thatrepresents the maximum flying height that will result in an acceptableread or write performance. The resolution value can be stored in amemory along with other resolution values for different areas of thedisk surface. For example, one stored threshold value can correspond toeach zone on the disk.

The first and second data patterns can be stored anywhere within thefirst track. In one embodiment, the patterns are stored in a servo dataregion of the first track. To decrease overhead on the disk, thepatterns can be stored in standard servo fields, such as the automaticgain control (AGC) field and/or the C/D servo burst fields.Alternatively, a dedicated servo field can be created for one or both ofthe patterns.

The disk drive can also include a unit for postponing the transfer ofuser data to the first track when it is determined that the head is notwithin the proper vertical distance range. For example, the first datapattern and the second data pattern can both be located in a servosector immediately preceding a data area on the first track. Thepatterns can be read by the reading device and then the determinationunit can determine whether the head is in the proper range. If the headis not in the proper range, the postponement unit can decide not to reador write data from/to the data area as the head proceeds to pass overthe data area from the servo sector. The postponement unit can thenperform a retry on the next revolution of the disk.

In one embodiment, the determination unit includes a transition detectorfor detecting indicia (such as, for example, peaks) in the second analogsignal portion that are indicative of magnetic transitions stored on thesurface of the disk. Because of the read signal resolution effect, whena relatively high frequency pattern is read by the head at an elevatedflying height, some of the resulting indicia will not be detectable bythe transition detector. Therefore, the number of indicia detected(and/or not detected) by the transition detector can be used as anindicator of flying height. The transition detector can include, forexample, an analog peak detector, a PRML channel, a decision feedbackequalizer, a finite delay tree search unit, or any other means fordetecting indicia in a read signal.

In another aspect of the present invention, a disk drive is providedthat includes a unit for determining whether the head is currentlywithin an acceptable vertical distance from the disk surface forperforming a transfer of user data between the predetermined track andthe exterior environment before a transfer of user data is allowed tooccur, wherein the determination does not include means for changing acurrent vertical distance between the head and the disk surface, and atransfer unit for performing the transfer of user data only when thehead is determined to be within the acceptable vertical distance by thedetermination unit.

The determination unit operates in substantially real time so that therequired determination can be made before the transducer reaches thedata area to/from which data is to be transferred. The determinationunit can make the required determination based upon read signalresolution or any other method capable of real time operation. Inaddition, the determination unit can include a comparison unit or peakdetection unit as described above.

In yet another aspect of the present invention, a disk drive is providedcomprising: a disk having a plurality of concentric tracks, the diskincluding a first pattern having a first frequency and a second patternhaving a second frequency, the second frequency being greater than thefirst frequency; a head for use in transferring data to/from the disk;means for reading the first pattern using the head to create a firstanalog waveform having a first magnitude value; means for reading thesecond pattern using the head to create a second analog waveform havinga second magnitude value; <combining unit for combining the firstmagnitude value and the second magnitude value to create a read signalresolution related value; and a comparison unit for comparing the readsignal resolution related value to a threshold value.

In one embodiment, the threshold value is based on a minimum read signalresolution that will produce an acceptable data transfer performance inthe disk drive. The combining unit can include a means for finding aratio between the first magnitude and the second magnitude. Thecomparison unit can include a storage unit for storing a plurality ofthreshold values corresponding to different areas on the disk surfaceand a retrieval unit for retrieving one of the threshold valuescorresponding to a track currently being accessed.

In still another aspect of the present invention, a disk drive isprovided comprising: a disk having a plurality of concentric tracks, thedisk including a first track having a first data pattern with a firstfrequency; a head for use in transferring data to/from the disk; meansfor reading the first data pattern, using the head, to produce an analogread signal having a predetermined number of peaks representative ofdata on the disk surface; a processing unit for processing the analogread signal to determine which of the peaks in the analog read signalmeet a predetermined detection criterion, wherein less than all of thepredetermined number of peaks will meet the predetermined detectioncriterion when the head is not within the desired flying height rangedue to relatively low read signal resolution at the first frequency, theprocessing unit creating an output signal; and a determination unit fordetermining whether the flying height of the head is within the desiredrange based on the output signal of the processing unit.

In one embodiment, the processing unit determines how many of the peaksin the analog read signal meet the predetermined detection criterion andthen compares the resulting peak count value to a threshold count value.As described above, the comparison unit may include a data storage unitfor storing at least one, and preferably a plurality, of threshold countvalues. In addition, the determination unit can include a comparisonunit for comparing the peak count value to a table of predeterminedcount values each having an associated flying height value to determinean actual present flying height value. The first data pattern caninclude, for example, a constant frequency data pattern or a variablefrequency data pattern, such as a chirp or random pattern, that includesthe first frequency. In addition, the processing unit may include atransition detector as described above.

In a further aspect of the present invention, a disk drive is providedthat includes a read channel including a determination unit fordetermining whether a head is within an acceptable vertical distancefrom a disk surface for performing a transfer of user data between atrack of the disk and an exterior environment. In one embodiment, thechannel, including the determination unit, is implemented on a singlesemiconductor chip. In another embodiment, the channel includes anoptimization unit for optimizing the channel for performing thedetermination function by changing the value of at least one of thechannel parameters during a period when the determination unit isperforming the determination function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a disk drive system that canutilize features of the present invention;

FIG. 2 is a sectional view of a disk and an associated head (having ahead slider) illustrating the flying height of the head above the disksurface;

FIG. 3 is a diagram illustrating data storage patterns on a disk surfacein accordance with one embodiment of the present invention;

FIG. 4 is a waveform illustrating portions of an analog read signal inaccordance with one embodiment of the present invention;

FIG. 5 is a block diagram illustrating a flying height determinationapparatus in accordance with one embodiment of the present invention;

FIG. 6 is a diagram illustrating data storage patterns on a disk surfacein accordance with another embodiment of the present invention;

FIG. 7 is a diagram illustrating data storage patterns on a disk surfacein accordance with yet another embodiment of the present invention;

FIG. 8 is a diagram illustrating a flying height determination apparatusin accordance with another embodiment of the present invention; and

FIG. 9 is a waveform illustrating portions of an analog read signal inaccordance with another embodiment of the present invention.

DETAILED DESCRIPTION

The present invention relates to a system for detecting head flyingheight variations in a disk drive in real time. That is, the systemallows head flying height to be checked on the fly while a correspondingread or write operation is being performed. In this way, read and/orwrite operations can be postponed whenever it is determined that thecurrent flying height of the head is outside a normal flying heightrange. Although the system may be used in virtually any type of datarecording system that uses a head to read/write information to arecording medium, the system is of particular value in systems that uselow flying height head elements, where even small variations in flyingheight can degrade performance significantly. As used herein, the termlow flying height head encompasses both contact heads and pseudo-contactheads.

FIG. 1 is a block diagram of a disk drive system 10 which can utilizefeatures of the present invention. As illustrated, the disk drive system10 is coupled to an external host unit 12 for performing disk storageand retrieval operations under the control of the host 12. The diskdrive 10 includes: a disk 14, a spin motor (not shown) for rotating thedisk 14, an actuator arm assembly 16, a head 18, a voice coil motor 20,a channel 22, an interface 24, a disk controller unit 26, and a servocontrol unit 28. The controller 26 is operative for controlling theoperation and timing of the other elements in the disk drive system 10.The interface 24 is operative for managing the flow of data to/from thehost unit 12 and receiving commands from the host unit 12 for deliveryto the controller 26. The channel 22 is operative for processing dataflowing between the host 12 and the disk 14. For example, during a readoperation, the channel 22 receives an analog read signal from the head18 and converts this to a digital signal which is recognizable by thehost 12. During a write operation, the channel processes a digitalsignal from the host 12 and converts it to a variable write currentsignal which is delivered to the head 18 for storage on the disk 14. Theactuator arm 16 carries the head 18 at a distal end for positioning thehead 18 above the disk 14. The voice coil motor 20 is operative forimparting motion to the actuator arm 16 during read and write operationsto position the head 18 above a desired track on the surface of disk 14.The voice coil motor 20 is responsive to a servo control signal fromservo control unit 28 that controllably positions the actuator arm 16based on the location of the track requested by the host 12 in a recentaccess request.

In a preferred embodiment of the present invention, the head 18 is a lowflying height head. The general trend in disk drives today is to designheads that ride closer to the disk surface than heads have in the past,i.e., low flying height heads. By riding closer to the disk surface, lowflying height heads produce less spacing loss and are able to read/writedata on the disk with greater definition, thereby allowing more data tobe stored in a given area on the disk surface. Low flying height heads,however, are generally more sensitive to variations in head flyingheight than are heads of the past. That is, in general, the performanceof a low flying height head that normally flies at 2 microinches will bedegraded to a much larger extent if the flying height of the head istemporarily increased by 2 microinches than would the performance of ahead that normally flies at 5 microinches.

To exacerbate the problem, low flying height heads are more likely toexperience variations in flying height than are higher flying heightheads. For example, low flying height heads are more likely to pick upparticles from the disk surface that increase the flying height of thehead than are heads that fly at higher heights. That is, debris orlubrication material on the disk surface may attach to the underside ofthe head, resulting in a greater flying height due to increased liftfrom the debris/material or contact between the debris/material and thedisk surface. The undesirable debris/material usually stays on the headfor a short period of time causing a temporary flying height increase.

As described above, the invention is capable of detecting variations inhead flying height in substantially real time. FIG. 2 is a sectionalview illustrating what is meant by the term “flying height.” Asillustrated in the figure, during operation, the head 18 (which, asillustrated, includes a slider) is raised above the surface of the disk14 by a spacing 30 known as the flying height of the head 18. Thespacing 30 is created by the interaction between air currents above thedisk 14, caused by rotation of the disk 14, and the aerodynamicqualities of the head slider. The slider is generally designed to keepthe head within a certain predetermined flying height range duringoperation of the disk drive. When the head 18 is outside of this flyingheight range, the performance of the disk drive 10 can be seriouslycompromised. For example, if the head 18 is too high above the surfaceof the disk 14 (i.e., the flying height is too large), the magneticfields produced by the head 18 will not be strong enough at the disksurface 14 to properly store the required magnetic transitions. Thisresults in a recorded signal on the surface of the disk 14 that is weakand potentially unreadable by the head 18 during a subsequent readoperation. Similarly, if the head 18 is too far above the surface of thedisk 14, the head 18 may not be able to read previously written data onthe surface of the disk 14.

To detect flying height variations in real time, the present inventionrelies upon variations in read signal resolution with flying height.Read signal resolution is a performance measurement that is related tothe disk drive's ability to read information at different frequencies.In this regard, read signal resolution is generally calculated using theratio of the magnitudes of two analog read signal portions havingdifferent frequencies. For example, to measure read signal resolution, aburst having a first frequency can be read from the disk surface tocreate a first analog signal portion and then a burst having a second,higher frequency can be read from the disk surface to create a secondanalog signal portion. The read signal resolution can then be calculatedbased upon the ratio of the magnitude of the second signal portion tothe magnitude of the first signal portion. To maintain an accurateresolution measurement, both bursts have to be read at substantially thesame head flying height. In conceiving the present invention, it wasdiscovered that read signal resolution varies with head flying height inan inverse manner. That is, as the flying height of the head increases,the read signal resolution for the head decreases. This is because headperformance at elevated frequency levels degrades more rapidly withincreased flying height than does head performance at lower frequencylevels.

FIG. 3 is a diagram illustrating the informational content of a portionof a disk surface in accordance with one embodiment of the presentinvention. As illustrated, the surface portion includes a plurality ofdata regions 32 that are periodically interrupted by servo positioninginformation portions 34. It should be appreciated that although thepresent embodiment of the invention is implemented in a system using anembedded servo scheme, the invention can also be implemented in systemsusing dedicated or hybrid servo schemes. The plurality of data regions32 are arranged in concentric tracks on the disk surface. Each servopositioning information portion 34 includes, among other things, atleast one automatic gain control (AGC) field 40 centered on acorresponding track and a plurality of servo positioning bursts (i.e.,an A burst 42, a B burst 44, a C burst 46, and a D burst 48) for use byservo unit 28 in positioning the head 18 above the track. It should beappreciated that other servo information may also be present in eachservo positioning portion 34 of FIG. 3 in accordance with the presentinvention. However, for purposes of convenience and clarity, theillustrated servo positioning portion 34 has been limited to theelements shown.

The AGC field 40 is used by the disk drive 10 to, among other things,set the gain of the channel 22 during read operations. That is, the head18 reads the AGC field 40 and uses the magnitude of the resulting analogread signal to determine the optimal gain of the channel 22. Asdescribed above, the servo bursts 42-48 are used by the disk drivesystem 10 for, among other things, positioning the head 18 above thedisk 14. The A/B bursts 42, 44 are used primarily during track followingoperations (i.e., maintaining the head 18 over the corresponding track)and the C/D bursts 46, 48 are used primarily during seek and settlingoperations (i.e., moving the head 18 from one track to another). Ingeneral, the A, B, C, and D bursts 42-48 are each comprised of aplurality of successive, equally spaced magnetic transitions on thesurface of the disk. As these transitions are read by the head, asubstantially periodic analog read signal is created. The frequency ofthe resulting read signal is related to how closely the transitions arepacked in the corresponding burst, i.e., how many transitions occur in agiven angular portion of the disk. As used herein, the “frequency” of aburst refers to the frequency of the analog read signal that resultsfrom the sensing of the burst by the head 18.

In past systems, the frequency of the AGC field 40 was the same as thefrequency of all of the other bursts 42-48. In accordance with oneembodiment of the present invention, the C burst 46 and the D burst 48are recorded on the surface of the disk 14 at a frequency that is higherthan the frequency of the AGC field 40 and both the A burst 42 and the Bburst 44. Therefore, when the head 18 is centered on one of the tracks,it is possible to find a magnitude of the analog read signal for boththe AGC burst 40 and either the C burst 46 or the D burst 48, dependingupon which one is centered for the particular track. FIG. 4 illustratesportions of an analog read signal resulting from the reading of an AGCfield 40 and a C or D burst 46, 48. As illustrated, the C/D portion ofthe signal is at a higher frequency than the AGC portion of the signal.Consequently, the magnitude of the AGC portion is greater than themagnitude of the C/D portion. The ratio between the frequency of the AGCfield 40 and the frequency of the C/D burst 46, 48 is chosen to providea measurable change in resolution for flying height changes of interestat all disk locations. In addition, the frequency of the C/D burst canbe different at different track locations (i.e., zoned) to optimize themeasurable resolution change.

FIG. 5 is a block diagram illustrating an apparatus 50, in accordancewith the present invention, for determining whether the head 18 iswithin a proper flying height range using the analog signal portions ofFIG. 4. In one embodiment of the present invention, the apparatus 50 islocated within the channel 22 of the system 10. For example, theapparatus 50 can be implemented on the same semiconductor chip as thechannel 22. Alternatively, the bulk of the operations performed byapparatus 50 can be implemented in firmware in the controller 26.

The apparatus 50 includes: AGC circuitry 51, a magnitude detector 52, aregister 54, a resolution measurement unit (RMU) 56, a comparator 58,and a random access memory (RAM) 60. As illustrated in FIG. 5, theapparatus 50 receives the analog read signal from the head 18 at aninput 62. The AGC circuitry 51 receives the analog read signal frominput 62 and normalizes the magnitude of other portions of the readsignal to the magnitude of the AGC portion of the signal. The AGCcircuitry 51 then delivers the processed read signal to the magnitudedetector 52 and to other circuitry in the channel. Under the control ofthe controller 26, the magnitude detector 52 first measures themagnitude of the AGC portion of the analog signal. The magnitude of theAGC portion is then delivered to the register 54, under the control ofthe controller 26, where it is stored for later use. The magnitudedetector 52 then measures the magnitude of the C/D portion of the analogread signal. The magnitude of the C/D portion and the stored magnitudeof the AGC portion are next delivered to the RMU 56 for calculation ofthe read signal resolution. The resulting read signal resolution valueis then compared, in comparator 58, to a threshold resolution value,stored in RAM 60, corresponding to the portion of the disk 14 beingaccessed. The threshold values stored in the RAM 60 represent the readsignal resolutions at the maximum head flying heights that will resultin an acceptable performance of the disk drive system 10. Each valuestored in the RAM 60 corresponds to a different area on the disk surface(such as, for example, a different zone, track, or sector.) The outputof the comparator 58, therefore, is indicative of whether the presentflying height of the head 18 is adequate for the performance of a readand/or write operation.

This flying height indication is delivered to the controller 26 whichmakes a decision as to whether the corresponding read/write operationshould be postponed. If a decision is made to postpone the operation,the controller 26 will ignore the subsequent data area 36 (that is, thedata area 36 following the present servo portion 34) and attempt to“retry” the read/write operation when the disk rotates to a point wherethe servo portion 34 and the data area 36 once again pass under the head18. If, after repeated passes, the head 18 does not fall within theprescribed flying height range, the controller 26 will determine that anerror condition exists and can indicate such to the host. Alternatively,the controller 26 can initiate remedial action designed to overcome apresumed cause of the defective flying height. For example, thecontroller 26 can initiate a routine designed to remove any foreignmatter from the air bearing surface of the head 18. Also, the controller26 can perform a write operation ignoring detection of the high flyingcondition and then perform a read operation on the same data todetermine whether it was properly written. Furthermore, for writeoperations, the data can be moved to a new location and the defectivelocation can be marked bad.

In one embodiment of the present invention, the need for additionalcircuitry can be reduced or eliminated through efficient use of the AGCcircuitry 51 of the channel 22. As described above, the function of theAGC circuitry 51 is, in general, to normalize the magnitude of otherportions of the read signal to the magnitude of the AGC portion of thesignal. Therefore, the AGC circuitry 51 normalizes the C/D portion ofthe signal to the magnitude of the AGC portion, by amplification. Themagnitude of the normalized C/D burst can then be measured and compareddirectly to a predetermined threshold value in RAM for that track (orportion of the disk). This reduces circuit complexity and cost since itis not necessary to measure the amplitude of the AGC portion 40.Therefore, by efficient use of the AGC circuitry 51, the presentembodiment can be implemented with little or no additional circuitry andsome additional firmware.

Because the present approach only requires a change in the frequency ofthe C and D bursts, on-track servo following is not affected. That is,the A and B bursts are used in the same manner that they are used inprior art servo systems. The C and D bursts, which are normally usedduring seeking and settling functions, are also used in substantiallythe same manner that they were used in the prior art. That is, eventhough an elevated frequency is being used for the C and D bursts, therelative magnitudes of the corresponding read signal portions should besubstantially the same.

In another embodiment of the present invention, as illustrated in FIG.6, a dedicated D burst 48 is used that is continuous across the disksurface. That is, the D burst extends across all of the tracks and isexclusively used to determine the read signal resolution of the head 18.This technique allows a head flying height determination to be madewhile the head 18 is either on or off the track. As in the priorembodiment, the present embodiment does not affect trace followingoperations, but could affect seeking and settling operations due to thefact that only a single quad (i.e., C or D) burst is available.

FIG. 7 illustrates a servo pattern in accordance with yet anotherembodiment of the present invention. As illustrated, the servo patternincludes an E burst 62 extending across the surface of the disk. Onlythe E burst 62 will have a frequency that is greater than the otherbursts. That is, the AGC field 40 and the A, B, C, and D bursts 42-48will all have the same frequency, while the E burst 62 will have anelevated frequency. Read signal resolution will be measured insubstantially the same manner as described previously, except that thehigher frequency signal portion will result from the E burst 62. Becausethis embodiment does not change any of the A to D bursts 42-48, trackfollowing, seeking, and settling operations are substantiallyunaffected. However, the addition of servo burst E 62 adds overhead tothe system and requires a change in the current ASIC chip controllingthe servo field strobes.

FIG. 8 illustrates an apparatus 70 in accordance with another embodimentof the present invention. The apparatus 70 is capable of detectingwhether the head 18 is within an acceptable flying height range basedupon the number of peaks (or other indicia) in an analog read signalthat are detected (or not detected) by a transition detector. As theflying height of the head increases, the read signal resolutiondecreases causing a decrease in read signal amplitude at higherfrequencies. Therefore, when a pattern having an elevated frequency isread by the head at a relatively high flying height, the reduced readsignal resolution can result in an analog read signal that has a numberof peaks (or other indicia) that are undetectable by a transitiondetector. The number of peaks that are detectable, therefore, can beused as an indication of the flying height of the head 18. The apparatus70 counts the number of detected peaks and uses the count to determinewhether the head 18 is at a proper flying height. The apparatus 70 canbe implemented in the channel 22, in the controller 26, or in anotherlocation in the disk drive 10.

The apparatus 70 includes: a transition detector 72, a counter 74, and arandom access memory (RAM) 76. During operation, the head 18 reads adata pattern from the surface of disk 14 and delivers a resulting analogread signal to the transition detector 72. The transition detector 72 isused to detect events in the analog read signal, such as peaks,indicative of magnetic transitions stored on the disk 14. The transitiondetector 72 creates an output signal indicative of the location of peaks(or other indicia of magnetic transitions on the disk) in the analogread signal. In general, most transition detectors only indicate thedetection of a transition if, among other things, the magnitude of theanalog read signal exceeds a predetermined threshold value at aparticular point in the signal. Therefore, if the magnitude of theanalog read signal is reduced due to resolution effects, sometransitions in the read signal will not be detected by the transitiondetector 72. In one embodiment of the present invention, thepredetermined threshold value is optimized so that read signals below aspecific resolution value do not produce detectable transitions.

The counter 74 receives the output signal of the transition detector 72and counts the number of detected peaks in the output signal. Thecounter 74 then delivers the count value for the pattern to thecontroller 26. At approximately the same time, the RAM 76 outputs atleast one calibration value, corresponding to the particular datastorage location on the disk 14 that is currently being accessed, to thecontroller 26. The controller 26 processes the count value and thecalibration value to determine whether the head 18 is within the desiredflying height range. In at least one embodiment, the controller 26 usesthe input values to generate an actual flying height value for the head18. If the head 18 is not within the desired flying height range, thecontroller 26 can postpone or cancel the current read/write operationusing read/write enable line 78.

The data pattern which is stored on the surface of the disk 14 inconjunction with the embodiment of FIG. 8 may take any of a number ofdifferent forms. In one approach, for example, the pattern is a constantfrequency pattern having an elevated frequency, such as those discussedearlier with respect to servo bursts C, D, and E. In another approach, arandom pattern is used that results in a peak count that is directlyproportional to the flying height. In general, the random pattern isdetermined by empirical methods and is longer than the constantfrequency pattern discussed above.

In yet another approach, a data pattern having a linearly increasingfrequency (i.e., a chirp pattern) is used. FIG. 9 illustrates an analogread signal resulting from the reading of such a chirp pattern. As seenin the figure, the magnitude of the analog read signal decreases as thefrequency of the signal increases. This is due to the resolution effect.The magnitude will eventually decrease to a point where peaks can nolonger be detected by transition detector 72. The controller 26determines the point in the pattern (and, therefore, the cutofffrequency) at which peaks in the analog read signal cease to bedetected. The controller 26 then determines whether the present flyingheight of the head 18 is proper based upon the detected cutofffrequency. Alternatively, the controller 26 can determine whether thepresent flying height is proper based on a peak count as describedabove. The length of the chirp pattern in any. particular implementationwill depend on the range of expected flying heights as well as theability to correct for head radius using read channel detection leveladjustments. In this regard, the length of the chirp pattern generallyfalls somewhere between the constant frequency pattern and the randompattern. It should be appreciated that other variable frequency datapatterns may also be used in accordance with the present invention.

The calibration values stored in the RAM 76 can include, for example:(i) count threshold values representing the minimum number of detectedpeaks that will result in an acceptable performance of the disk drive10, (ii) cutoff frequency threshold values representing minimum peakdetection frequencies that will result in an acceptable performance ofthe disk drive 10, and/or (iii) flying height threshold valuesrepresenting maximum flying heights that will result in an acceptableperformance of the disk drive 10. To determine whether the head is inthe desired flying height range, the controller 26 can compare, forexample, the count value from the counter 74 to the appropriate countthreshold from the RAM 76. Alternatively, if a chirp pattern is beingused, the controller 26 can compare the detected cutoff frequency to theappropriate cutoff frequency threshold value in the RAM 76. In addition,or alternatively, the RAM 76 (or another memory) can include look-uptables for finding an actual flying height value corresponding to ameasured count value or cutoff frequency value. The actual flying heightvalue can then be compared to an appropriate flying height thresholdvalue stored in the RAM 76 for the particular area of the disk 14 beingaccessed. As an alternative to the look-up table approach, the RAM 76can include parameters from which an appropriate flying height equation(as a function of measured count value or cutoff frequency value) can besynthesized for each area of the disk surface.

As described above, the transition detector 72 is used to detect eventsin the analog read signal, such as peaks, indicative of magnetictransitions stored on the disk 14. In this regard, the transitiondetector 72 may include virtually any type of transition detectiondevice commonly used in digital data storage systems such as, forexample, analog peak detector circuitry, partial response/maximumlikelihood (PRML) circuitry, decision feedback equalizer (DFE)circuitry, and finite delay tree search (FDTS) circuitry. The transitiondetector 72 can be the same detector used in the channel 22 to createthe digital output signal which is transferred to the host 12 or it canbe a dedicated unit which is specifically implemented to perform theflying height determination function. The counter 74 may include anytype of digital counting unit that can be controlled by the controller26 or other controlling means. In one embodiment of the invention, thecounter 74 and the RAM 76 are implemented within the controller 26.

In general, the channel 22 in a disk drive system will have a number ofvariable parameter inputs which affect the performance of the channel22. The values applied to these variable parameter inputs will affect,for example, the ability of the system to detect flying heightvariations. In one embodiment of the present invention, the valuesapplied to the variable parameter inputs of channel 22 are changedwhenever a flying height determination is being performed. That is,channel parameter values are applied to the channel 22 which optimizethe channel for the performance of the flying height determination andare then changed back to normal channel parameter values, optimized forperforming read operations, after the flying height determination hasbeen made. For example, it may be determined empirically that theoptimal transition detector threshold value for flying heightdetermination is somewhat greater than the threshold value which isoptimal for general transition detection. While the head 18 is readingthe relevant pattern on the disk 14 during the flying heightdetermination, the controller 26 can cause the threshold value of thetransition detector to be changed to the optimal flying height value. Inone embodiment, a random access memory is provided for storing optimalflying height channel configuration values for all areas of the disksurface.

Although the present invention has been described in conjunction withits preferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art readily understand.For example, the patterns used to determine or sense read signalresolution do not have to be located within the servo portion of thedisk surface but, alternatively, can be located in a data region on thedisk. This can be useful, for example, in a system using dedicated servotechniques. In addition, the AGC field 40 can be modified to includeboth the high and the low frequency patterns used to determine the readsignal resolution. For example, an alternating pattern of high and lowfrequencies can be implemented in the AGC field 40 so that the channelcan set its gain using the low frequency portion and measure read signalresolution using the high frequency portion. Such modifications andvariations are considered to be within the purview and scope of theinvention and the appended claims.

What is claimed is:
 1. A disk drive, comprising: a disk having aplurality of concentric tracks for storing data, the tracks including afirst track having a random data pattern; a head for reading data fromand writing data to the disk; and a detection circuit that determineswhether the head is within an acceptable flying height range in responseto a peak count that is based on the random data pattern and issubstantially proportional to the flying height of the head.
 2. The diskdrive of claim 1, wherein the random data pattern is determined byempirical methods.
 3. The disk drive of claim 1, wherein the random datapattern is located in an AGC field.
 4. The disk drive of claim 1,wherein the peak count is directly proportional to the flying height ofthe head.
 5. The disk drive of claim 1, wherein the detection circuitincludes a transition detector and a counter, and an output of thetransition detector is coupled to an input of the counter.
 6. The diskdrive of claim 5, wherein the transition detector detects a transitionin a detection signal based on the random data pattern only when thedetection signal exceeds a predetermined threshold value.
 7. The diskdrive of claim 6, wherein the counter counts the number of transitionsin the detection signal detected by the transition detector and providesthe peak count.
 8. The disk drive of claim 7, wherein the detectioncircuit includes a memory, and the memory provides a calibration valuecorresponding to a data storage location on the track that is accessedduring one of a read and write operation while the random data patternis read to provide the detection signal.
 9. The disk drive of claim 8,wherein the detection circuit determines whether the head is within anacceptable flying height range in response to the peak count and thecalibration value.
 10. The disk drive of claim 9, wherein the detectioncircuit postpones the operation if the detection circuit determines thatthe head is not within an acceptable flying height range.
 11. A diskdrive, comprising: a disk having a track for storing data, wherein thetrack includes a random data pattern; a head for reading data from andwriting data to the disk; and a detection circuit that includes atransition detector and a counter, wherein the detection circuitdetermines whether the head is within an acceptable flying height rangein response to a peak count that is based on the random data pattern andis substantially proportional to the flying height of the head, and anoutput of the transition detector is coupled to an input of the counter.12. The disk drive of claim 11, wherein the transition detector detectsa transition in a detection signal based on the random data pattern onlywhen the detection signal exceeds a predetermined threshold value. 13.The disk drive of claim 11, wherein the counter counts the number oftransitions in the detection signal detected by the transition detectorand provides the peal count.
 14. The disk drive of claim 11, wherein thedetection circuit includes a memory, and the memory provides acalibration value corresponding to a data storage location on the trackthat is accessed during one of a read and write operation while therandom data pattern is read to provide the detection signal.
 15. Thedisk drive of claim 14, wherein the detection circuit determines whetherthe head is within an acceptable flying height range in response to thepeak count and the calibration value.
 16. The disk drive of claim 11,wherein the detection circuit postpones a data transfer operation if thedetection circuit determines that the head is not within an acceptableflying height range.
 17. The disk drive of claim 11, wherein the randomdata pattern is located in an AGC field.
 18. The disk drive of claim 11,wherein the detection circuit determines whether the head is within anacceptable flying height range while the head is at a substantiallyconstant flying height independently of flying height data obtained fromthe disk drive at other than the substantially constant flying height.19. The disk drive of claim 11, wherein the detection circuit determineswhether the head is within an acceptable flying height independently offlying height data obtained from the disk drive at a predeterminedflying height.
 20. A disk drive, comprising: a disk having a track forstoring data, wherein the track includes a random data pattern; a headfor reading data from and writing data to the disk; and a detectioncircuit that determines whether the head is within an acceptable flyingheight range in response to a peak count that is based on the randomdata pattern and is substantially proportional to the flying height ofthe head while the head is at a substantially constant flying heightindependently of flying height data obtained from the disk drive at apredetermined flying height and independently of flying height dataobtained from the disk drive at other than the substantially constantflying height.